Conventionally, it is often the case where surface properties of a metallic base material are enhanced by thermally spraying metallic powder or the like to a surface of the metallic base material. This thermally spraying method can be performed relatively easily and hence, the thermally spraying method has been widely applied to various kinds of members. Particularly, the thermally spraying method has been used in various industrial fields as an effective technique when it is necessary to partially impart corrosion resistance and wear resistance to a surface of a metallic base material. In general, as a powder material which is used as thermal spraying powder to be thermally sprayed to a surface of a metallic base material, an Ni-based self-fluxing alloy, a Co-based stellite alloy and the like are used.
However, although the Ni-based self-fluxing alloy, the Co-based stellite alloy and the like exhibit excellent adhesiveness with abase material, a thermal-sprayed layer formed by such materials improves material properties thereof by solid-solution strengthening or precipitation hardening and hence, these materials are insufficient in terms of corrosion resistance and wear resistance of the thermal-sprayed layer.
On the other hand, with respect to ceramic which is considered to exhibit excellent corrosion resistance and wear resistance, cracks are liable to occur in a thermal-sprayed layer due to porosity of a skin film so that the thermal-sprayed layer is liable to be peeled off from the base material.
In view of such circumstances, there has been proposed a thermal-sprayed film which is made of a cermet having properties between properties of metal and ceramic. Particularly, a WC-Co cermet material is, because of its high hardness, used in applications which require wear resistance. However, the WC-Co cermet material has a drawback that a counterpart material is abraded.
Further, a cermet material which contains a composite boride of Ni, Mo or W is used from a viewpoint of reduction of abrasion of a counterpart material, the cermet material has a drawback in terms of corrosion resistance and wear resistance when the cermet material is brought into contact with a resin which generates a highly corrosive gas such as a molten fluororesin or PPS.
Patent document 1: JP-A-8-104969